import numpy as np
import random

a = np.arange(20)
print(a)
print(a[[1,3,5,7,9]])


b = np.arange(20).reshape(4,5)
print(b)
print(b[0, 2:4])
print(b[0, b[0]>2])
print(b[[1,3],:])
print(b[[1,3],:][:,[1,3]])
